The objectives of the proposal are to test the following hypotheses: a) Enzyme replacement therapy of lysosomal storage disease (e.g. Tay-Sachs, Gauchers disease) is best achieved if the missing enzyme is presented to cells in a kind of biological "spansule" (liposome) which has surface ligands to engender uptake by cells possessing specific receptors. b) That uptake of Ig-coated liposomes by phagocytes from patients with Tay-Sachs disease or peroxidase deficiency into their lysosomal system provides the means to bring enzymes into every organ and tissue, since circulating leukocytes percolate through these after emigrating from post-capillary venules. That the experimental model we have already exploited, peroxidase deficiency of Mustelus canis, can be used to test this enzyme delivery system. c) That means can be found selectively to release the newly acquired enzymes from the lysosomal system of circulating phagocytes without generalized cytotoxicity, immunogenicity of the foreign protein, and with some tissue specificity. d) That Ig-coated liposomes exceed in their capacity to correct enzyme deficits in man and experimental animals the capacity of free enzymes or of enzymes entrapped in uncoated liposomes.